The 1/e myth, was Re: [e2e] TCP Local Area Normal behaviour? any

[Cannara]

Not sure I get why your response is so energetic, Noel.  I think I said that $
motivated much of the decisionmaking in networking devices, which seems to be
exactly the reason we all now have $20 switches everywhere there are more than
two $10 interfaces!  

Sure, there are few true Ethernet segments anymore, except in the backplane
logic of switches.  Having recently worked for a manufacturer of these chips,
the contention issues that used to be solved on a shared bus, still need to be
solved, but within a shared switch, and with a capability to slow any node
connected to the switch's ports (backpressure).  

I also don't get your reference to Full Duplex, perhaps it's a straw man --
yes FDX Ethernet links aren't doing CSMA/CD, but something more traditional in
telecom:  access control via in/out-of band signalling (e.g. Pause Frames). 
So, indeed, I agree "FDX Ethernet" is a misnomer.  The deal is that Ethernet
framing has become a standard, while that name itself implies the traditional
access method (CSMA/CD) as well, so there can be confusion.

Alex


Noel Chiappa wrote:
> 
>     > From: Cannara <cannara at attglobal.net>
> 
>     > seeing how CSMA/CD is superior to any token-passing system,
> 
> You really don't want to get into this.
> 
> In any event, it's kind of OBE, since most "CSMA/CD" systems these days are
> anything but. Rather, they are usually actually hosts connected directly to a
> bunch of switches, the whole kit-n-kaboodle linked together by point-point
> links, all of which happen to use an access protocol that looks like
> CSMA/CD. The latter being picked, of course, rather than something designed
> for the purpose, since that was the dominant market technology at the time the
> whole concept of "LAN based on inert transmission medium" became another dusty
> page of computing history (along with rotationally optimizing assemblers,
> etc), and it was easier to just adopt that, rather than have to replace all
> the host interfaces.
> 
> <Irony_mode>
> By the way, what is this "full-duplex" stuff people keep talking about?
> I've never heard of a CSMA/CD network that supported full-duplex
> operation.
> </Irony_mode>
> 
> Anyone out there actually still have an Ethernet which actually is a long
> coax cable with hosts hooked to it via transceivers? No, I didn't think
> so...
> 
>     > the spike in token's heart is not just cost per node, but that the
>     > crossover moves to higher access rates as nodes are added, meaning
>     > that CSMA/CD becomes better, relatively, as LAN segments have more
>     > nodes.
> 
> Your model seems to leave out a few factors which weigh against real
> CSMA/CD (not the ersatz simalcrum people are using these days, see
> above), such as network physical size. Gee, what a shock - you obviously
> not having any axe to grind one way or another between the two
> technologies.
> 
>         Noel